Question

Why is NH4 ion formed?

Why does nitrogen have to bond with 4 hydrogen atoms? Wont it be happy if it will only bond to just 3 hydrogens to begin with? I mean, NH3 is already stable so why is NH4 formed? I find polyatomic ions very confusing. I will be really grateful if you can help me out. Thankyou!

Answer 1

Ammonia `NH_3` behaves as a nucleophile accepting a proton from water or acid molecule on the basis of a co-ordinate bonding.

Explanation:

When ammonia `NH_3` molecule `color(blue)"dissolves in water or reacts with an acid (ex: HCl)"`, it behaves as a nucleophile or as a Brønsted–Lowry base by `color(blue)"accepting a proton"`, `H^+`, from a water molecule. So,

`color(blue)"=>`The ammonium ion, `N H^+"_4`, becomes `color(green)"positive"`.

A covalent bond is formed by two atoms sharing a pair of electrons between the N and the 4th-H forming a `color(blue)"Co-ordinate (dative covalent) bond"`. The hydrogen's electron is left behind on the chlorine to form a negative chloride ion.

Once the ammonium ion has been formed it is impossible to tell any difference between the dative covalent and the ordinary covalent bonds.

NOTE:
Co-ordinate bonding:
A covalent bond is formed by two atoms sharing a pair of electrons. The atoms are held together because the electron pair is attracted by both of the nuclei.

This bond is formed because
Nitrogen has 1 lone pair of electrons, and
Hydrogen ion has 0 electrons, but 1 proton